The rapid development of optoelectronics has produced a desire for methods of producing nanometer-sized patterns on semiconductor surfaces. Typically, these patterns are etched into semiconductor substrates by a number of techniques. For example, wet chemical etching has been used to etch a wide variety of semiconductors. Typically, for the case of II-VI semiconductors such as ZnSe, wet chemical etching utilizes bromine-based chemistries. Wet chemical etching proceeds by oxidation of the semiconductor constituents followed by chemical dissolution of the oxides in suitable solvents. Wet chemical etching can be isotropic and the uniformity of the process is low. Production industries in the optoelectronics. industries require more controlled etching procedures than can be achieved using wet etching.
As a result of the shortcomings of wet chemical etching, dry etching processes have been developed for semiconductors. For example, plasma-etching has been used to produce etching profiles in silicon substrates. Plasma-etching involves generating chemically reactive species, radicals, ions, and electrons at low pressure in a reactive gas mixture in a reactor with the aid of an electric discharge. The reactive species, radicals, ions generated in this manner are accelerated towards a substrate by means of an electrical field. The ions fall virtually vertically onto the substrate, and promote the reaction of the reactive plasma species with the silicon substrate. An etch mask can be applied to the substrate prior to etching to allow the ions to etch a pattern into the substrate. Because of the nearly vertical fall of the positively-charged particles, etching is much more slow on the side-walls the etched substrate as the etching progresses.
To further protect and passivate the side-walls, polymer formers, which are added to the plasma at selected times during etching, can be used to protect the side-walls of the etched structure by means of a formed polymeric film. This method has been used to anisotropically etch silicon substrates.